Artificial joints generally require mechanisms to control their movement. For example an artificial knee joint or prosthetic joint will be prescribed for a person with a through-knee (TK) or an above-knee (AK) amputation, i.e. a person without a knee joint, shank or foot. The ability for the knee to bend or articulate during sitting, kneeling or ambulating is desirable. It is also desirable to have the ability to control the leg during the swing-phase of the gait when the person is walking or running. By improving control you also improve the look of the gait and make the gait look more natural. Finally the joint has to provide sufficient support to the person.
When standing or putting weight on the leg, as during the support-phase or stance-phase of the gait cycle it is undesirable for the artificial joint to bend uncontrollably as this will cause the amputee to fall. This is referred to as “stance-phase control”. Amputees have some control during stance by the way they load the leg and how they use their remaining muscles at the hip. Alternatively, a prosthetist can align a prosthesis to be more or less stable by placing the knee joint axis behind the load bearing plane or load line. However, this tends not to produce ideal gait characteristics. While many different designs have been proposed, the majority of prosthetic knee joints are designed to address the issue of stance-phase control, i.e. keeping the knee from articulating when the prosthesis is supposed to be providing support. A prosthetic knee joint may have a built-in “locking” mechanism for this purpose.
The “swing-phase control” refers to the control of the joint's movement or articulation during the swing phase of the gait cycle to make the gait more efficient and more natural looking. Traditionally pneumatics or hydraulics are used in prosthetics to help control the swing-phase, as they are velocity dependent. Therefore as the gait velocity changes, the knee resistance changes. This is a beneficial attribute, because greater resistance is needed at higher velocities to provide adequate control of the joint. For example during walking, the air in a first chamber of a cylinder of a traditional pneumatic mechanism begins to compress as the knee begins to bend at the beginning of the swing-phase. Some of the air is displaced into a second chamber on the opposing side of the cylinder. A valve is used to control the flow rate and therefore the resistance. However the compression of the air in the first chamber also acts like a spring. The damping resistance and compressed air spring force act to slow the progression of knee flexion until the knee begins to extend. This acts to bring the leg forward quicker and limits the amount of heel-rise to normal levels. As the leg is extending, the air in the second chamber now compresses and before the knee fully extends, acts as a cushion (in the same manner as before) to slow the knee extension. This prevents the leg from slamming into the extended position (referred to as terminal impact). A hydraulic mechanism works in a similar manner but does not provide a spring force as the fluid is incompressible.
Prior art artificial joints have addressed some of the noted issues for both stance and swing-phase control. For example, many knees utilize hydraulic mechanisms to provide stance/swing-phase control including those described in U.S. Pat. Nos. 5,376,137, 6,658,540 B1 and 6,652,585 B2. These devices address how the hydraulic mechanism is controlled to provide very high resistance to flexion during stance, and lower resistances to flexion and extension during swing. However the prior art does not address a swing-phase controller that efficiently functions within an artificial joint having a dual axis (knee flexion axis and control axis) stance-phase controller.
Thus a swing-phase controller with an artificial joint which controls the swing-phase of the joint through a large range of motion, is light weight, compact, low cost, produces more efficient and natural looking gait, can be used in other applications such as orthotic and robotic, decreases wear on other components in the artificial joint, and does not interfere with the stance-phase mechanism of the artificial joint is desirable.